This renewal application requests five years' support for work now in continuous progress for over 15 years at Washington University. Dr. John Boineau, the new PI, has replaced Dr. James Cox, the former P1, who transferred to Georgetown University Hospital. Dr. Cox remains as a special consultant. The broad aims continue to be the direct or surgical ablation of cardiac arrhythmias. The emphasis of the current renewal is focused upon the development of a new procedure, the radial incisions approach (RIA), to eradicate atrial fibrillation (AF) and restore atrial transport function and is directed primarily toward patients undergoing surgery for valvular or ischemic heart disease. Conventional valve or CABG surgery does not eliminate and may not prevent AF in these patients. The availability of an effective means of eradicating this arrhythmia in these patients at the time of surgery would permit control of rate and rhythm, limit embolic stroke, and improve cardiac performance, outcome, and the quality of life. Whereas the Maze and RIA assume randomly distributed and changing reentry which are eliminated without prior activation mapping, new data indicate that some forms of AF result from (spatially) stable reentry which can be identified by new mapping methods and focally ablated. Thus, a second project is directed toward map guided, focal cryoablation of AF. This could be performed off bypass as a more limited and rapid alternative to the more extensive and (bypass) time consuming RIA procedure. A third project is targeted at prevention and correction of postoperative atrial flutter (AFL) after the Fontan operation in congenital heart patients or after lung transplant surgery. Studies will be performed in both realistic animal models with atrial enlargement and patients with AF and AFL and will center about the use of new automated, 3-D mapping techniques and rapid numerical analysis of potentials recorded simultaneously from to 512 electrodes during the arrhythmias. Preliminary observations indicate that the proposed studies are feasible, will provide new information regarding the different mechanisms of AF and AFL that are related to atrial enlargement and/or atrial surgery, and this data will be used to develop the new surgical ablation techniques to control or prevent these arrhythmias.